Monolithic Integrated Micro-Thin-Film Thermocouples for On-Chip Temperature Measurement of GaN HEMTs

Gallium nitride (GaN) is crucial in power devices due to its wide bandgap, high electron mobility, and high critical field. GaN devices, such as high electron mobility transistors (HEMTs), are vital for high-power and high-frequency applications and can withstand high temperatures. However, these devices could encounter self-heating effects at high power, causing current collapse and performance degradation. The accurate temperature monitoring in GaN devices is essential for maintaining performance and avoiding failures. Micro-thin-film thermocouples (micro-TFTCs) offer a solution with their high-resolution and direct temperature measurements. These thermocouples, integrated onto device surfaces, bypass the limitations of other methods. In this work, we demonstrate the monolithic integration of micro-TFTCs into GaN HEMTs, using a platinum-chromium junction with a sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$19.23~\pm ~0.405~\mu $ </tex-math></inline-formula>V/°C. This enabled precise monitoring of GaN HEMT channel (channel width <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$= 200~\mu $ </tex-math></inline-formula>m) temperatures, with a measured temperature of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$68.54~^{\circ }$ </tex-math></inline-formula>C <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm ~0.16~^{\circ }$ </tex-math></inline-formula>C at a power density of 5.72 W/mm, highlighting the effectiveness of this technique in thermal characterization of semiconductor devices.